1. Field of the Invention
This invention relates to an electrophotographic apparatus of the type where toner is thermally fixed on a recording medium, and especially to an electrophotographic apparatus permitting fail-free fixing irrespective of the type of recording medium.
An electrophotographic apparatus is equipped with a cylindrical photoreceptor, a primary charger for charging a surface of the photoreceptor, an exposure light source for forming a latent electrostatic image on the photoreceptor, a developing device for applying toner to the latent electrostatic image to develop the same, a transfer charger for electrostatically attracting the toner from the photoreceptor to a recording medium so as to achieve transfer of the toner, a cleaning device for removing any toner still remaining on the surface of the photoreceptor, a fixing unit for fixing the toner image on the recording medium, and a feed mechanism for feeding the recording medium.
The primary charger charges the surface of the photoreceptor to impart photosensitivity to the surface. Next, the exposure light source illuminates the photoreceptor to form a latent electrostatic image on the surface of the photoreceptor. The developing device then applies toner in accordance with the latent electrostatic image on the surface of the photoreceptor so that a toner image is formed. Subsequently, the toner image is transferred onto the recording medium by the transfer charger.
Recording media, such as normal paper sheets, stored in a paper supply tray are fed out one by one from the tray along a usually curved guide path in accordance with rotation of the feed roller and are then delivered to the transfer charger in synchronization with rotation of the photoreceptor. After the toner image has been transferred at the transfer charger, the recording medium is subjected to thermal fixing at the fixing unit so that the toner image is fixed on the recording medium.
On the other hand, special media such as envelops or postcards are each conveyed horizontally to the transfer charger via a guide path or route into which such special media are manually inserted. These special media are therefore conveyed without bending. Each special medium with a toner image likewise transferred thereon by the transfer charge, is fed to the fixing unit, where thermal fixing is conducted similarly.
The above-described electrophotographic apparatus permits printing on a wide variety of media, including recording media, such as general paper, and special media such as envelops and postcards. However, for this purpose, the fixing unit normally must be set at a fixing temperature sufficiently high to fix toner images on various media without failure. Namely, its fixing temperature must be set at a level sufficiently high so that fixing is feasible even on recording media having a large thickness and poor fixation such as envelops and postcards.
Fixing is therefore always performed at the high temperature set in view of media having poor fixation properties despite that fixing can be conducted at a lower temperature when general or normal paper is being printed. Accordingly, when a general recording medium such as normal paper is being used, electricity is wasted and, moreover, curling of the recording media occurs.